The invention relates to a cassette for use in connection with a device for printing characters on a surface from the stroke impact of an endless dye impregnated ribbon such as a typewriter.
Generally, cassettes using an endless typewriter ribbon have been used for typewriters and, particularly, high-speed typewriters. Within the cassette, transport means are provided to move the ribbon in correspondence with the typing process and to retain the ribbon substantially stretched in the stroke region of the typewriter. The length of the ribbon is selected to provide an opportunity to re-impregnate the ribbon before each part of it is typed on a further time. This, of course, extends the useful life of the ribbon.
Generally, it is estimated that an ordinary textile typewriter ribbon having a width of about 6.35 mm and a length of about 13 m can be used to print legibly about 600,000 to 800,000 characters at a typing rate of about 30 characters per second. Based on this, such a ribbon is completely used up over a period of about 8 hours, about a normal working day. A more careful study indicates that the time for re-impregnating the actual typing region of the ribbon from the adjacent area is usually not sufficient so that the actual performance is not as good as the estimated performance.
One prior art attempt to improve the useful life of the cassette ribbon utilizes inking rollers along the path of the ribbon within the typewriter. It has been determined that without the use of pressure or centrifugal force, very little ink is communicated from the inking rollers to the ribbon in contact therewith.
Another prior art attempt to overcome the problem utilizes a sponge saturated with ink and disposed within the cassette in contact with the ribbon. This embodiment did not use any storage area for the ribbon and relies on the continuous contact of the ribbon with the sponge to achieve re-impregnating of the ribbon. The results obtained have been unsatisfactory.
Generally, the re-impregnating of a ribbon with dye during the use of the ribbon presents some difficulty because the stroke impact compresses the ribbon during the typing process and thereby disturbs the physical properties of the ribbon in the vicinity of impact.